What is a SOUL.md persona?
3 min read
A SOUL.md persona is a structured file that captures how a specific person writes: their phrasing, their rhythm, and the words they would never use. Quillen builds one from your own writing and checks every draft against it, so replies sound like you rather than like a generic assistant.
What a SOUL.md captures
Most AI writing tools give you a tone dial: friendly, professional, casual. A tone dial changes the surface and leaves the structure of the writing untouched, which is exactly what makes assisted replies read as assisted. A SOUL.md goes deeper, modelling one particular person rather than a setting.
- Voice fingerprint: the phrasing and sentence rhythm you actually use
- Antivocabulary: the words and cliches you never use, so drafts avoid them
- Formatting habits: how you open, break lines, and close
- Intent: the kinds of points you make and the stance you take
How Quillen uses it
Quillen reads your existing posts or a few writing samples and synthesizes the SOUL.md for you, with a completeness meter that tells you how well it knows you so far. You do not write the file by hand.
Every draft the agent generates is then linted against that persona. A draft that does not sound like you is flagged and held rather than sent, and the edits you make in review feed back in, so the next draft is closer. The file is the reason a reply can be automated without collapsing into the same agreeable voice everyone else is using.